Investigating Flavourful New Physics at the TeV Scale

Abstract

We investigate the possibility of new physics at the TeV scale coupled mainly to the third generation. This arises naturally when trying to address the Standard Model flavour puzzle together with the Higgs hierarchy problem. We show, in a pure Effective Field Theory approach, that this scenario is perfectly compatible with current experimental data, while also being able to accomodate some deviations from the Standard Model observed in semileptonic B decays. From a model-building perspective, we focus on so-called 4321 models, based on a SU(4) × SU(3) × SU(2) × U(1) gauge symmetry, which feature quark-lepton unification at the TeV scale. These models have been generically shown to be the common last step in a sequence of symmetry breakings in deeper UV theories explaining the Standard Model flavour structure. We study important phenomenological implications of 4321 models in the context of leptonic τ decays and electroweak precision tests. Lastly, we analyse the issue of the Higgs mass stability with respect to quantum corrections in generic multi-scale models of flavour.